best Methods of producing artificial Cold. 273 
to be, snow or pounded ice twelve parts, common salt five 
parts, and of nitrous ammoniac, or a powder of equal parts 
sal ammoniac and nitre mixed, five parts ; or one-third of com- 
mon salt, when I used that alone, with snow or pounded ice. 
My apparatus then (Dec. 28th last) consisted of two vessels 
(fig, 3. and 4 ); an instrument, (fig. 6 .) to grind or rather 
scrape the ice to powder ; a kind of spatula (I use a marrow- 
spoon) to stir the powder occasionally ; a thermometer (fig. 8.); 
and a small thermometer glass with the bulb three-fourths 
full of quicksilver (fig. 7.). I filled the vessel, fig. 3, holding 
when inverted two pints, stratum super stratum, with pounded 
ice, common salt, and a powder consisting of equal parts sal 
ammoniac and nitre mixed together; by first putting in six 
ounces of pounded ice, then two ounces and a half of common 
salt, and, after stirring these well together, two ounces and a 
half of the mixed salts, mixing the whole well together ; this 
was repeated in the same manner until the vessel was quite 
full ; it was then tied over securely with a wet bladder, turned 
upright, and one ounce and a half of rain water poured into 
the tube through a funnel, the tube covered with a cork, and 
the .vessel left undisturbed till the water was frozen perfectly 
solid. The instrument for grinding it was then put in to ac- 
quire cold, whilst the vessel, fig. 4, holding a pint, was filled in 
the same manner, with the same proportions of materials, a 
bladder tied over it, set upright, and one ounce of fuming 
nitrous acid poured in to be cooled. The ice was then ground 
to powder, and when -finished, the .nitrous acid being found to 
have acquired a sufficient degree of cold, viz. — 13 0 , the fri- 
gorific mixture of ice and salts was let out of the vessel which 
contained the nitrous acid ; and the powdered ice (still sur- 
